In the field of bundle bottle wrapping, the use of plastic film is widely known.
A traditional and widespread method provides the use of heat-shrinking plastic film. In particular, a film of heat-shrinking plastic material is wound around an array of four/six bottles, arranged side by side to form an assembly of two/three bottles on two rows, which is then subjected to an oven to cause the shrinking of the film and thus form a compact and stable bundle.
The stability of this bundle is a fundamental feature, if one takes into account the—often rough and careless—handling which it undergoes during the transfer from the manufacturing site to the purchasing sites of shopping centres and from these to the purchasers' homes.
A widely acknowledged drawback of this solution is given by the fact that the cost of this type of wrapping is relatively high. In fact, in order to obtain the desired resistance and stability features, a heat-shrinking plastic material with a thickness of 30-40 μm, of a weight of 5 to 8 gr/sqm, and hence already due to this rather expensive, is employed; in addition to that, the use of a heat-shrinking oven in turn implies non-negligible installation and energy consumption costs.
WO99/14122 discloses a bundling machine wherein, regardless of the film used, no continuous functioning is obtained, but it is provided to first divide the bottles into single assemblies of a predetermined number of pieces, to subsequently wrap with film the single assembly. EP 708 028 discloses a similar solution. The number of bottles of the bundle in this case is predetermined and, to be able to change it, it is necessary to act replacing a series of mechanic members, in particular the templates which define the bottle position.
EP2202186 also discloses a bundling machine which acts discontinuously, winding with plastic film the individual bottle assemblies, after having separated them from the mass of fed bottles.
In order to offer an alternative solution, bundle wrapping apparatuses have already been proposed—at least at a theoretic level—which resort to stretching plastic film. For example, EP 197 574 discloses a different solution for package wrapping—which may also be bottle packages—with stretching film, that is, film which does not need to undergo heat-shrinking.
This solution consists in causing a sequence of bottle assemblies to advance continuously, along a feeding line, and to cause them to be wound around by a stretching film laid as a continuous spiral, subsequently providing to severe the packages one from the other through a severing device.
However, in the introductory part of this patent it is detailed that such a continuous spiral winding has the drawback that, by effect of the oblique winding of the film, the members contained in each assembly—especially if they are cylindrical-surface bottles—undergo a twisting effect, which tends to warp the final package and hence to decompose the alignment between the bottles, with the effect of a possible package opening.
For this reason, the object of the invention disclosed in EP 1 431 185 is a machine capable of sequentially performing two windings, one above the other: the former as a continuous spiral and the subsequent one—after the cutting and the severing of the package—on the package itself rotated by 90° with respect to the others.
EP 197 574 discloses another similar machine, wherein the winding of the plastic film is accomplished through two reels inclined in an opposite way with respect to the transport line.
Also WO2012/055490 discloses a winding apparatus with plastic film, where two film coils are used. However, no specific arrangement is provided for effectively obtaining a final bundle, neither in connection with the entering step of bottles, nor in the step of the removal and severing of the individual bundle.
As can be clearly understood, although at a theoretic level these machines have merits over heat-shrinking film apparatuses, at a practical level various drawbacks exist.
The main one derives from the fact that the stretching film, as known, is suitably stretched before the application, undergoing great elongation, up to the order of 300%; from this stretching a corresponding elastic shrinking force derives, which is the one which normally ensures the integrity of the package even in difficult transport and displacement conditions. As a result this force—which acts also immediately after the application of the first film—causes that, in particular, a package which has been severed from the reminder before the application of the second film undergoes a twisting force which may cause the warping thereof, even with release of the contents, that is, precisely that effect which one aimed to avoid.
On the other hand, reducing the film winding tension and the resulting stretching—to avoid the forming of excessive twisting forces—is not a viable solution, because a reduced stretching of the film would cause both an undue consumption of material, and a residual elongation of the material which would make bundle management unpleasant for the final user, and a lack of containment forces which are instead necessary for maintaining securely together the bundle containers. A remarkable improvement of this wrapping technique with stretching film has been reached with the process disclosed in Italian patent application no. MI2011A001543 in the name of the same Applicant. Here it is suggested to feed the bottles to the wrapping station in a continuous and compact manner, causing them to progress until beyond the wrapping station with a suitable guiding slide, forming then a single helical wrapping with stretching film, and separating said continuous wrapping into short segments, that is, into individual bundles, in a cutting station located downstream of the winding station.
Although the process described here has substantially effectively solved the problem of the prior art, it has been seen that margins for further improvement exist. In particular, it has been detected that, in order to manufacture a stable bundle, it is important to avoid any bottle misalignment as long as the bundle wrapping has been completed. This action can hardly be performed on the bottles being wrapped, because there is the risk of interference with the film winding members.
EP 1 495 973 discloses a dragging and indexing system of a mass of bottles, which acts through a pair of wheels, provided with peripheral recesses with which part of the container body engages. U.S. Pat. No. 5,979,147, DE 383 94 98 and EP 2 415 695 disclose similar apparatuses, wherein there are provided wheel means or moving bars provided with engaging members for sorting and indexing the bottles along the displacement path.